It is sometimes necessary to machine in place existing equipment for the purpose of testing, repairing and/or reconditioning the equipment. This process may be a result of the original fabrication of the machine or testing thereof, machine breakdown or malfunction, or may be part of a repair or maintenance program to overcome normal wear and tear or to prevent a malfunction of the equipment.
For example, relatively large piping which may be part of a pipeline, building, plant machinery, ship or other structures/devices, can include overlays which are a result of a welding process during the initial fabrication of the piping, or a repair or maintenance of the equipment. The overlays are basically weld buildup rings, or weld crowns, of inconel (a hard, tough material), or other material, around the outer perimeter of the piping or piping component such as a nozzle or valve, in the vicinity of the weld. The necessity of providing a juncture on a pipe that is professionally finished with a defect-free weld has been appreciated for some time, and more particularly in the case of nuclear power plants and pipelines, for example, the necessity of providing junctures that are reliable and durable is of the utmost importance. Consequently, the weld crowns need to be smoothed out in order for testing equipment to be used to check for cracks, wall thickness, etc. Further, the equipment size, location and connection to other structures may determine that it is advantageous to machine the equipment in place, rather than remove it from its operational configuration for refurbishment.
A known method of smoothing out the weld crowns is to use an axial feed slide mounted to a “clamshell” and cut or machine the overlay. Clamshells are portable pipe lathes that are connected to the outside of the pipe, where the cutting tool can move around the outside perimeter of the pipe to machine the outside of the pipe. Such devices are known in U.S. Pat. Nos. 4,739,685, 4,939,964, 5,549,024 and 6,619,164, for example. One problem with this method is that the machine would cut round and most overlays are not perfectly round. Because of this, more material has to be removed than necessary to get the entire overlay to be smooth. This also requires extra time.
The time element can be critical in pipelines, nuclear reactors, and the like, where downtime can be very costly and the necessity of providing junctures that are reliable and durable is of the utmost importance. Frequently, the working conditions associated with the pipe machining equipment have been quite hostile either to the machine or to the machine operator. For example, in nuclear reactors, the necessity for pipe replacements has been such that these types of maintenance procedures are required quite frequently. However, maintenance personnel may only work in an area that is radioactively hot for extremely short periods of time. Accordingly, the desirability of an apparatus for finishing pipes which can be set up in a minimal amount of time, can complete the machining in a minimum of time, and can be initialized and dismantled in a minimal amount of time has obtained increasing importance and acceptance in the industry.
What is needed in the art is an apparatus and method of machining an exterior surface of equipment, particularly piping, that can machine in place existing equipment and which can smooth weld crowns or other elements that may not be perfectly round, or perform other machining, efficiently.